US2581446A

US2581446A - Supporting means for vacuum electrodes

Info

Publication number: US2581446A
Application number: US124641A
Authority: US
Inventors: Charles F Robinson
Original assignee: Consolidated Engineering Co Inc
Current assignee: Consolidated Engineering Co Inc
Priority date: 1949-10-31
Filing date: 1949-10-31
Publication date: 1952-01-08
Anticipated expiration: 1969-01-08

Description

Jan. 8, 1952 c. F. ROBINSON SUPPORTING MEANS FOR VACUUM ELECTRODES Filed Oct. 31, 1949 JNVENTOR. 0/4245: xFfloa/Msml,

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Patented Jan. 8, 1952 SUPPORTING MEANS FOR VACUUM ELECTRODES Charles F. Robinson, Pasadena, Calif., assignor to Consolidated Engineering Corporation, Pasadena, Calif., a corporation of California Application October 31, 1949, Serial No. 124,641

This invention relates to vacuum tubes and more particularly, to improvements in electrode mounting within such tubes.

The invention provides a complete and simple solution to the troublesome problem of supporting electrodes in precise geometrical relation within a vacuum system. The difiiculty arises from the fact that such electrodes must be insulated from each other and yet preferably mounted to each other to insure a fixed spatial relationship. Thus, to achieve geometrical precision, it is desirable that the electrodes be tied together in some fashion, it being virtually impossible to maintain a fixed spatial relationship between independently mounted electrodes. Moreover, in many instances, as for example, mass spectrometry, it is desirable to tie the electrodes together as a unit for the additional reason that such construction simplifies removal of the electrodes from the vacuum system. A mass spectrometer having such a unitary electrode assembly and incorporating the structure of the present invention is described in detail with respect to the drawing.

The use of insulating ties or spacers suggests itself as one possible solution. However, any insulation serving as a structural member in a vacuum system in the presence of electrical fields must satisfy the following requirements:

1. The insulation must not liberate gas into the system either by inherent vapor pressure or by porosity at temperatures ranging between about 100 C. and 500 C.

2. The insulation must be dimensionally stable at temperatures in the above range.

3. The insulation must not carbonize or track when subjected to ion or electron bombardment or electrical flashovers.

4. The insulation should be inexpensive. That is. it should be capable of being fabricated to close tolerances or should be available commercially at close tolerances and at low cost.

13 Claims. (01. 313-81) The first three of the above requirements eliminate plastics and virtually every other insulating material except glass, synthetic sapphires, fused quartz, or similar vitreous refractories. However these materials in the forms of tubing, rods, sheets, or other special shapes do not satisfy the dimensional limitations of the fourth requirements since commercially available forms are generally molded to very loose tolerances, and if held to close tolerances, are very expensive.

Very recently, vitreous refractories, such as Pyrex glass and synthetic sapphire mono-crystals have, become commercially available in spherical form to very close tolerances in the order of magnitude of plus or minus .00005 of an inch.

I have now developed an electrode mounting arrangement wherein these spherical refractories are used to space and also to locate a plurality of electrodes within a unitary structure. The invention provides, in a vacuum tube having a plurality of electrodes, means for holding the electrodes in fixed geometrical relationship comprising a plurality of insulating spacers separating the electrodes and clamping means: clamping the electrodes against the spacers. Various modifications are made in the above arrangement for particular applications. For example, it is frequently necessary, as in the case of mass spectrometry, to shield any insulating surfaces from an ion beam, etc., with a conductive shield. Various means for accomplishing such shielding are illustrated in the accompanying drawing in which: i

Fig. 1 is a sectional elevation showing a plurality of electrodes mounted together in accordance with the invention; and

Fig. 2 is a sectional elevation through an ion source of a mass spectrometer with the electrodes of the ion source being held in fixed geometrical relationship in accordance with the invention.

Fig. 1 shows the general principles of the mounting means of the invention and comprises a plurality of electrodes ill, I I, l 2, held to a single tie plate M by means of a plurality of tie bolts l6, extending through the tie plate and screwed into the outermost electrode l0. Prior to assembling the electrode structure, the several electrodes and tie plate are drilled in a jig to form the holes 10A, IDB in electrode II), the holes HA, H3 in electrode ll, holes IZA, [2B in electrode l2 and holes MA, MB in tie plate [4. Although shown in the drawing as being aligned, the holes in the several electrodes need not be thus arranged provided only that adjoining electrodes are provided with aligned holes. However, alignment through all the electrodes constitutes preferred practice since it reduces the drilling to a.minimum and also tends to insure more accurate results since only a single jig need be employed.

A glass ball of the type described and of somewhat larger diameter than the holes in the electrodes is placed between adjacent electrodes to seat in the aligned holes therein. Thus, a glass ball 98 is interposed between electrodes l0 and l I seating in the aligned holes IDA, HA. A second glass ball [9 is interposed between the same electrodes seating in the other aligned holes IIJB, MB in these two electrodes. To insure stability, three or more such spacers are provided between each pair of electrodes and seating in similar aligned holes. A third spacer ball 20 is partially apparentbetween the electrodes Ill and II. In a similar fashion, electrodes l I and I2 are spaced from each other and are accurately held in fixed geometrical relationship by a plurality of glass balls, and the electrode 12 is similarly arranged with respect to tie plate 16. There need be no direct connection between tie plate [6 and the intermediate electrodes II and I2, a single series of tie bolts clamping the outermost electrode H] to the tie plate will hold all of the electrodes together since the spacer balls [8, I9, 20, etc., hold the electrodes in fixed position, there being no possibility of lateral shift.

The accuracy with which the electrode positions are predetermined is afunction of the ac.-

' pattern is an important advantage of the invention. It is frequently desirable andsometimes necessary, to dismantle such an electrode structure for cleaning and repairs. With an arrangement as shown in Fig. 1, such procedure is a simple matter involvingonly the removal of the tie-bolts I6, I7 and separation of the electrodes. When the unit is reassembled the electrodes will inherently bear the same geometrical relationship to each'other with .a possible error of only .0001 of an inch. There is no other electrode-structure in use today which can be dismantled and re assembledwith such case and such accuracy. Even greater accuracy may be achieved by peening the corners of the .drilled holes to the radius of the spacing balls in asimple hydraulic oriimpact press using commercially available highly accurate .carbolly or. other suitable ball for the peening hammers. r

The spacing between the electrodescan becpreselected .within very broad limits. Pyrex balls ranging in size from to A, of an inch are available commercially, permitting electrodes spacing of from about A,; of an inch to approximatelyv Man inch or greater without adopting special techniques. If desired, closer spacing can be; obtained with oversized balls, as for ex,- amplal/ of an inch separation may be obtained with inch balls by countersinking one of the seating holes.

Although the arrangement show in Fig. 1 illustrates the electrodes as having the seating holes extending all the way through the electrode, and the several seating holes in the separate electrodes are all aligned from top to bottom ofthe stack, neither of these features is a limitation on the invention. It is apparent that all that is required is a very shallow hole in which the'spacing balls may seat and it is not necessary that the spacing balls between the electrodes l0 and H seat in continuationsv of thesameholes in which the spacing balls betweenthe electrodes H and I2 are located. However, from a manufacturing standpoint, it isconvenient to stack the electrodes. and tie plate in a jig and drill through the stack to form the arrangement shown in Fig. 1.

The invention. is particularlyapplicable to use in the ion source of a mass spectrometer. As is well known, a mass spectrometer is an analytical instrument for sortingand measuring ions according to their mass-to-charge ratio. Such a trodes.

mass spectrometer includes an ion source in which the molecules of a gas sample are ionized by bombardment with an electron beam or by other known methods and are propelled from'the ionizing region and into an analyzer tube by means of pusher and accelerating electrodes. The usual arrangement includes a pair of coplanar pusher electrodes through which gas molecules are introduced into the path of an electron beam, a first accelerating electrode having a slit therein through which the ions, as they are formed, are propelled under the influence of a potential between the pusher and first accelerating electrode and a second and third accelerating electrodes through which the ions pass, being accelerated in their travel between'the several electrodes. To establish different potentials onthe several electrodes, it is, of course, necessary that they be insulated from each other. Recent developments in mass spectrometry have resulted in an ion source, in which all of the electrodes are mounted from a single insulated mounting plate by, separate tie rods, the tie rods connected to any given electrode passing through oversized holes in the intermediate electrodes.

'An ion source generally similar to that described above is illustrated and described inv considerable detail in co-pending United States patent application, Serial No. 33,596, filed by Clifford E. Berry on June 17, 1948, now Patent No. 2,548,859, granted April17, 1951. The ion source shownin this co-pending application is reproduced with certain modifications in sectional elevation in Fig. 2. Referring to this figure, the ion source comprises an insulating plate 22 a first conductive plate 23, a, second conductive plate 24 overlying the first plate and in engagement there- ,with and beinghollowed out to form an ionization chamber 26, and accelerating

electrodes

28 and 29. A sample inlet tube 32 extends through the insulating plate and first conductive .pl'ate, opening into the ionization chamber 26. A pair of 'pusherelectrodes 34, 34A are mounted in the ionization chamber 26 and are separated by a passageway 34B through which gas molecules pass from theinlet tube 32 into the region of the; ionization chamber above the pusher elec- A transverse electron beam originating from a source 36 is passed through ionization chamber to ionize the molecules therein. ,A potential difference is established between the pusher electrodes 34, 34A, the conductive plate 24 and the successive accelerating

electrodes

28, 29,. The function of this ion source is toionize sample molecules in the ionization chamber and to propel, them from the chamber through slits 21, 21A, 2B in the succeeding accelerating electrodes so that'they issue through the electrode 29 at a high velocity. Detailed description of the functioning of an ion source and of amass spectrometer would addnothing to an understanding of the invention.

Asmentioned above, it is necessary in an electrode structure wherein an ion beam is produced,

to shield any insulating surfaces from-the beam so that surface charges will not develop 'on such surfaces. -The development of surface'charges on insulating surfaces, the adverse effect of such surface charges on mass spectrometer operation contact with each other, may be welded together. However, the accelerating

electrodes

28 and 29 must necessarily be separated from the plate 24 and from each other. In Fig. 2 I have shown two methods of spacing these electrodes in accordance with the invention wherein the insulated balls are shielded or located so they cannot see the ion beam. Either of the two means shown in the drawing may be used to .the exclusion of the other, the single drawing serving merely to show the alternative means.

The electrode 28 is provided with an annular axially projecting shoulder 28A which extends into an annular groove 24A formed in the adjacent plate 24. The electrode 28 is drilled through the shoulder at 38, 39 and as many other locations as desired and the plate 24 is drilled to form the holes 40, 4| opening into the groove 24A. The

holes

38, 39 in the electrode 28 are aligned with the holes 40, 4|, respectively, in the plate 24 and

glass balls

44, 45 are seated in the two pairsof aligned holes in the same manner as shown in Fig. 1. It will be seen that there is no direct path between an ion beam passing through the slit 21, 21A, 21B and the

glass balls

44, 45.

To hold the

electrodes

28, 29 in fixed spatial relation, holes 48, 49 are drilled in the electrode 29, and holes 50, 5| are drilled in the electrode 29 in alignment with

holes

48, 49. The holes 50, ii are countersunk at their upper end and tubular members 54, 55 are affixed therein projecting upwardly toward the electrode 29. The inside diameter of the tubular members 54, 55 is equal, within very close tolerances, to the inside diameter of the

holes

44, 49 in electrode 29. A convenient way of forming this arrangement is to tap the upper surface of the electrode 28 and weld or press-fit a length of bar stock therein, having the outside diameter of the tubular members 54, 55. The

electrodes

28, 29 may then be placed in a jig and the holes 59, 5!, 48, 49 drilled therein and through the bar stock. The net result will be as shown in Fig. 2. The

holes

48, 49 in electrode 29 are likewise countersunk at their lower end and sleeves 58, 59 are afiixed therein as by swaging, welding or otherwise, the sleeves 58, 59 being of larger diameter than the corresponding tubes 54, 55 and projecting downwardly to encircle the upper ends of these tubes. Spacing balls 60, 6! are seated between the

holes

48, 49 and the corresponding tubes 54, 55, respectively, to insulate the two electrodes from each other and to fix their spacial relationship. Although the drawing of Fig. 2 illustrates only two spacing balls between each of the two electrodes, it is apparent that three or more spacers represent preferred construction since two balls will not prevent tipping of the electrode.

A plurality of tie rods 64, 65 are connected between the insulated plate 22 and the uppermost electrode 29, passing through oversized passageways in the intermediate conductive plates and electrodes. The tie rods 54, 65 are conveniently fused through the insulated plate 22 in the manner described in the aforementioned co-pending application and the electrode 29 is held thereon by nuts 66, 51, respectively. In this manner, the electrode 29 exerts a compressive force on the intervening electrodes which hold the spacing balls snugly, preventing any shift of the electrodes with respect to each other.

One major differentiating feature between the ion source illustrated in Fig. 2 and the ion source illustrated in said co-pending application is the matter of tying the electrodes to the insulating plate. In an attempt to achieve fixed geometrical relationship between the electrodes, it has been the practice heretofore to weld each of the electrodes to tie rods extending from the insulating plate. One big drawback of this type of construction is the dlfficulty of tearing down the structure for cleaning, etc., and re-assembly. Because of the use of the insulated spacers in accordance with the invention as shown in Fig. 2, there is no need to weld the tie rods 64, to the electrode 29 and in fact, there is no need of providing tie rods from the insulating plate to the intermediate electrodes since they are all clamped in position by the single group of tie rods and are held in this position by the spacing balls.

In Fig. 2, the pusher electrodes are shown diagrammatically only. They may be spaced from the plate 23 by means of spacing balls as shown in the same manner as in the diagram of Fig. l or in the manner of the

plates

28, 29. The simpler arrangement may be used since the spacers are not exposed to any ion beam, being effectively shielded by th pusher electrodes themselves. Separate tie rods must of necessity be used between the pusher electrodes and the insulating plate since the compressive force exerted between the insulating plate and the outermost electrode 29 has no effect on the pusher electrodes. In apparatus wherein separate tie rods are required for each successive electrodes, these tie rods are used also as electrical leads. In the apparatus shown in Fig. 2, the tie rods connecting the insulating plate and electrode 29 may be used as electrical leads in the same manner. Since, however, no tie rods are required between the plate and the intermediate electrodes, any type of rigid or non-rigid leads may be carried through the plate and connected with the appropriate electrodes.

The invention is not limited in accordance with the drawing and description thereof. Although the holes in adjoining electrodes are shown to be of equal diameter and to extend through the electrodes, they need not be formed in this manner. All that is necessary is that the adjoining holes in which a single spherical spacer is seated be coaxial and be deep enough to receive the spacer. If the holes are of different size the spacer will merely seat deeper in the face of one electrode than in the face of the adjoinin electrode. There will be no sacrifice of accuracy so long as the two holes are coaxial. Also, the mounting means shown in Fig. 2 whereby the spacers are shielded from the ion beam are not adapted exclusively to use in the ion source of a mass spectrometer. Other vacuum tubes in which insulating surfaces require shielding, as for example, electron guns, high frequency triodes, etc.. are preferably constructed using one or the other, or both, of the shielding means shown in Fig. 2.

I claim:

1. In a vacuum tube having a plurality of electrodes, means for holding the electrodes in fixed geometric relationship comprising a plurality of spherical insulating spacers disposed between adjacent electrodes and seating in spaced, axially aligned cavities formed in said adjacent electrodes, and clamping means clamping the electrodes against the spacers.

2. In a vacuum tube having a plurality of superposed electrodes, means for holding the electrodes in fixed geometric relationship comprising an insulating mounting plate, a plurality of spherical insulating spacers disposed between adjacent electrodes and seating in aligned 7 cavities formed in adjoinin faces of adjacent electrodes, and clamping means for clamping the electrodes between an outer electrode and the mounting plate, the clamping means being insulated 'from the intermediate electrodes,

3. In a vacuum tube, an electrode assembly comprising a plurality of electrodes having a-plurality of holes therein, the holes in one electrode being aligned with and the same diameter as the holes in an adjoining electrode, a plurality of spherical insulators disposed between the electrodes and seating in the aligned holes, and means clamping the electrodes together against said insulators so that the electrodes are spaced from each other by said insulators and held against lateral shift by-theinsulators seating in said'holes.

'4. In a mass spectrometer ion source having a plurality of electrodes with aligned slits therein for passage of an ion beam therethrough,'means for holding said electrodes in fixed geometric relationship comprising a plurality of sphericalins'ulators seating in aligned cavities in adjoining faces of adjacent electrodes, means preventing the spacers from seeing the ion beam and means clamping the electrodes against the spacers.

5. In a mass spectrometer ion source having a plurality of electrodes with aligned slits therein for passage of an ion beam therethrough, means for holding saidelectrodes in fixed geometric relationship comprising an insulating mounting plate, a plurality of spherical insulators disposed between adjacent electrodes and seating in cavities formed in adjoining faces of said adjacent 2.

through holes in the intermediate electrodes of larger diameter than the bolts.

7. In a mass spectrometer ion source having at least two plate type electrodes with aligned slits therein for passage of an ion beam therethrough,

means for spacing said electrodes-in fixed-geometric relationship comprising an annular groove in the adjoining face of one of said electrodes, an annular lip in the adjoinin face of the-other electrode extending into said 'groove without touching said one of said electrodes, a plurality of spherical insulators disposed in said groove and seating in aligned cavities formed in the bottom of said groove and outer face of said lip; and means clamping the electrodes against said-insulators.

8. Apparatus according to claim 7 wherein said cavities are formed by a plurality of aligned holes in each electrode opening into said groove and the outer face of said lip respectively.

9. In a mass spectrometerion sources having at least two plate type electrodes with aligned slits therein for passage ofan ion beam therethrough, means for spacing said-electrodes in fixed geometric relationship comprising a series of aligned pairs of holes in the electrodes, the several holes being countersunk in adjoining faces of the electrodes, a tubular member afllxed in the countersunk portion of each hole and projecting towardthe other electrode one of said tubular members of each aligned pairheing of larger diameter than the other tubular member of each pair and extending concentrically over the end of said other tubular. member without touching it, aplurality of spherical insulators disposed between said electrodes between the end of said other of said tubular members of each pair and the aligned hole in the adjacent electrode, and means for clamping the. electrodes against said insulators. '10. Apparatus according toiclaim 9 wherein the hole in the smaller tubular memberin each pair is the same diameter as the hole in the electrode carrying the companion tubularmember ofthe pair. 1

ii. In a vacuum tube having at leasttwo electrodes, means for spacing said electrodesin-fixed geometric relationship comprising an annular groove in the adjoining face of one of said electrodes, an annular lip in the adjoining face of the other electrode extending into said groove without touching said one of said electrodes, a plurality of spherical insulators disposed in said groove and seating in aligned cavities formed in the bottom of said groove-and outer face of-said lip, and means clamping the electrodes against saidinsulators. 1

12. In a, vacuum tube having at least twoelectrodes, means for spacing said electrodes in fixed,

countersunk portion of each hole and projecting toward the other electrode one of said tubular members of each aligned pair being of larger diameter than the other tubular member of each pair and-extending concentrically over the end of said other tubular member without, touching it, a plurality of'spherical insulators disposed between the end of said other of said tubular members of each pair and the'aligned hole'in-the adjacent electrode, and means for clamping the electrodes against said insulators. 13. Ina vacuum tube having a plurality of superposed electrodes, means for holding the electrodes in fixed geometric relationship comprising aninsulating mounting plate, a plurality of spherical insulating spacers disposed between adjacent electrodes andseatedi'n aligned cavities formed in adjacent faces of adjacent electrodes, mounting posts extending from the mounting plate through aligned holes in-the zseveral elecltrodes independent of the spacers, the aligned holes in the electrodes being larger than the, posts to provide an annular insulating'gap, and-clamping means affixed on the ends of the posts :and insulated from the proximate electrode to clamp the electrodes-against the spacers.

CHARLES F. ROBINSON.

REFERENCES CITED The following references are of record in'the is of this patent: V

V UNITED STATES PATENTS v Numher